
419
Bit 7
OVF
Description
0
[Clearing condition]
*Read TCSR when OVF = 1, then write 0 in OVFA
(Initial value)
1
[Setting condition]
When TCNT overflows (changes from H'FF to H'00)
When internal reset request generation is selected in watchdog timer mode, OVF is
cleared automatically by the internal reset.
Note: * When the interval timer interrupt is disabled and OVF is polled, read the state of OVF = 1
twice or more.
Bit 6—Timer Mode Select (WT/
IT): Selects whether the WDT is used as a watchdog timer or
interval timer. If WDT is used in watchdog timer mode, it can generate a reset when TCNT
overflows. If WDT is used in interval timer mode, it generates a WOVI interrupt request to the
CPU when TCNT overflows.
Bit 6
WT/
IT
Description
0
Interval timer mode: Interval timer interrupt (WOVI) request is sent to
CPU when TCNT overflows
(Initial value)
1
Watchdog timer mode: Internal reset can be selected when TCNT overflows*
Note: * For details of the case where TCNT overflows in watchdog timer mode, see section 11.2.3,
Reset Control/Status Register (RSTCSR).
Bit 5—Timer Enable (TME): Selects whether TCNT runs or is halted.
Bit 5
TME
Description
0
TCNT is initialized to H'00 and count operation is halted
(Initial value)
1
TCNT counts
WDT0 TCSR bits 4 and 3—Reserved: These bits cannot be modified and are always read as 1.
Bits 2 to 0—Clock Select 2 to 0 (CKS2 to CKS0): These bits select an internal clock source,
obtained by dividing the system clock () for input to TCNT.